As the information age advances, display devices for displaying information are actively being developed. More particularly, flat panel display (FPD) devices having a thin profile, light weight and low power consumption are actively being pursued to substitute cathode ray tube (CRT) devices. For example, a liquid crystal display (LCD) device, a plasma display panel (PDP), a field emission display (FED) device and an electroluminescent display (ELD) device have been researched and developed as an FPD device. Specifically, liquid crystal display (LCD) devices are widely used as monitors for notebook computers and desktop computers because of their high resolution, high contrast ratio, color rendering capability and superiority in displaying moving images.
A liquid crystal display (LCD) device relies on optical anisotropy and polarizability of liquid crystal molecules to produce an image. Due to the optical anisotropy of liquid crystal molecules, refraction of light incident onto the liquid crystal molecules depends on the alignment direction of the liquid crystal molecules. Liquid crystal molecules are aligned with directional characteristics resulting from their long, thin shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field thereto.
A liquid crystal display (LCD) module includes a liquid crystal display (LCD) panel having two substrates and a liquid crystal layer interposed therebetween and a backlight assembly supplying light to the LCD panel. The liquid crystal molecules are aligned according to the direction of an electric field generated between electrodes disposed on both substrates of the LCD panel. By refracting and transmitting incident light and controlling the electric field applied to a group of liquid crystal molecules within particular pixel regions, a desired image can be obtained. However, because an LCD panel does not emit light, an LCD module requires an additional light source. Accordingly, an LCD module includes a backlight assembly disposed below an LCD panel to supply light.
Of the different types of known liquid crystal display (LCD) devices, active matrix LCD (AM-LCD) devices, which have thin film transistors (TFTs) and pixel electrodes arranged in a matrix form, are the subject of significant research and development because of their high resolution and superior ability in displaying moving images. A cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) may be used as a light source of a backlight assembly.
In general, backlight assemblies may be classified into two types according to a disposition of the light source, such as a side-type and a direct-type. In a side-type backlight unit, a light guide plate (LGP) is disposed at a rear of an LCD panel and a light source is disposed at a side of the LGP. Light emitted from the light source is refracted in the LGP and is supplied to the LCD panel. In a direct-type backlight unit, a plurality of light sources are disposed at a rear of an LCD panel, and light emitted from the plurality of light sources is directly supplied to the LCD panel.
FIG. 1 is schematic cross-sectional view showing a liquid crystal display module using a direct-type backlight assembly according to the related art. In FIG. 1, an LCD panel 10 and a backlight assembly 20 are integrated in an LCD module by mechanical elements. Accordingly, the LCD module includes an LCD panel 10, a backlight assembly 20, a main frame 30, a top frame 40 and a bottom frame 50. The LCD panel 10 is disposed over the backlight assembly 20, and the main frame surrounds side surfaces of the LCD panel 10 and the backlight assembly 20. The top frame 40 surrounds a front edge surface of the LCD panel 10, and the bottom frame 50 wraps a rear surface of the backlight assembly 20. The top frame 40 and the bottom frame 50 are combined through the main frame 30.
The LCD panel 10 includes a first substrate 12, a second substrate 14 and a liquid crystal layer between the first and second substrates 12 and 14. Although not shown in FIG. 1, a driving circuit is connected to a side of the LCD panel 10 and is bent toward a rear of the LCD panel 10. The backlight assembly 20 includes a reflecting sheet 22, a plurality of fluorescent lamps 24 and an optic sheet 26. The reflecting sheet 22 has a white color or a silver color and is disposed over the bottom frame 50. The plurality of fluorescent lamps 24 are parallel arranged over the reflecting sheet 22, and the optic sheet 26 covers the plurality of fluorescent lamps 24. In addition, the optic sheet 26 may include a prism sheet and a diffusing sheet. As a result, lights emitted from the plurality of fluorescent lamps 24 and reflecting on the reflecting sheet 22 are supplied to the LCD panel 10 through the optic sheet 26. The brightness of the lights becomes uniform while passing through the optic sheet 26.
The backlight assembly 20 is optically designed to supply a uniform plane light having high quality to the LCD panel 10. One of the factors for the uniform light is to keep a distance “a” between the plurality of fluorescent lamps 24 and the optic sheet 26. When the distance “a” is too small, a linear light having a stripe shape reflecting the shape of each fluorescent lamps 24 is supplied to the LCD panel 10. In addition, when the distance “a” is too great, the brightness of the light is reduced. Accordingly, the distance “a” should be exactly controlled. Moreover, sizes of each fluorescent lamp 24 and the optic sheet 26 increase according to the increase of a display device in a size. As a result, a large-sized optic sheet may be partially sunk, and it is hard to keep the distance uniform in a large-sized LCD module.
To solve the above problems, an additional means adjusting the distance has been suggested. A rubber ring may be disposed on an outer surface of a portion of each fluorescent lamp 24 to adjust the distance. As sizes of each fluorescent lamp 24 and the optic sheet 26 increase, the distance between each fluorescent lamp 24 and the optic sheet 26 increases and the thickness and the width of the rubber ring increase. However, as the width of the rubber ring increases, the portion of each fluorescent lamp 24 that is blocked by the rubber ring is enlarged and light loss increases. As a result, the brightness is reduced at the blocked portion and non-uniformity in brightness is caused.
Recently, a lamp guide holder is used to keep the distance between the fluorescent lamp and the optic sheet uniform. In addition, the lamp guide holder prevents sway and break of the fluorescent lamp.
FIG. 2 is a schematic cross-sectional view showing a backlight assembly according to the related art. In FIG. 2, a reflecting sheet 22 and a lamp guide holder 60 are sequentially disposed over a bottom frame 50, and an optic sheet 26 is disposed over the lamp guide holder 60. The lamp guide holder 60 includes a horizontal part 62, a fixing part 64, a pair of lamp holding parts 66 and a supporting part 68. The fixing part 64 downwardly extends from a rear surface of the horizontal part 62, and the pair of lamp holding parts 66 is formed on a front surface of the horizontal part 62. The fixing part 64 passes through the bottom frame 50 to fix the lamp guide holder 60. Each lamp holding parts 66 has a ring shape having an open portion, and two adjacent fluorescent lamps 24 are inserted into the pair of lamp holding parts 66. The supporting part 68 having a cone shape upwardly extends from the front surface of the horizontal part 62 at a central portion. The supporting part 68 supports the optic sheet 26. The distance between the fluorescent lamp 24 and the optic sheet 26 is kept uniform by the lamp guide holder 60. In addition, the fluorescent lamp 24 is fixed to the pair of lamp holding parts 66 with a predetermined distance from the reflecting sheet 22. As a result, the possibility of sway and break of the fluorescent lamp is reduced.
However, since the pair of lamp holding parts 66 directly contacts the outer surface of the fluorescent lamp 24, the emission region of the fluorescent lamp 24 is partially blocked. The block of the emission region causes light loss and reduction of brightness.
FIG. 3 is a schematic plane view showing a brightness distribution in a backlight assembly having a lamp guide holder according to the related art. In FIG. 3, stains “B” having a relatively low brightness are inspected at a position corresponding to the lamp guide holder 60 (of FIG. 2).